We present a method to determine constructive and destructive interference areas on the object plane in partially coherent imaging. This method is based on the interference pattern on the image plane. A function Gamma that shows constructive and destructive interference areas with respect to the origin on the object plane is derived as the product of mutual intensity on the object plane and the Fourier transform of the pupil function. The convolution integral of Gamma and object transmittance gives the constructive and destructive interference areas. Experimental results show that small clear openings placed at constructive interference areas enhance light intensity at desired positions. By applying this method to optical microlithography imaging, one can achieve resolution enhancement of fine features with a relatively small amount of computation.